Adaptive modulation and coding (AMC), which adjusts at least one of the modulation scheme and the coding rate on an adaptive basis, is known as link adaptation in radio communication systems.
For example, in adaptive modulation and coding in long-term evolution (LTE), at least one of the modulation scheme and the coding rate of a downlink shared channel (PDSCH: Physical Downlink Shared Channel) is adaptively controlled based on channel quality indicators that are fed back from user terminals (see, for example, non-patent literature 1).
To be more specific, in adaptive modulation and coding in LTE, user terminals feed back channel quality indicators that correspond to the channel quality (for example, the SNR, the SINR, etc.) of signals from a radio base station, to the radio base station. The radio base station transmits the PDSCH by applying modulation schemes (for example, QPSK (Quadrature Phase Shift Keying), 16 QAM (Quadrature Amplitude Modulation), 64 QAM and so on) and coding rates that match these channel quality indicators fed back.